Ok, this needs Cabal to be tweaked as well, due to an overly optimistic unqualified import in Cabal :-)

libraries/Cabal/Cabal/Distribution/Simple.hs:412:7:
Ambiguous occurrence ‘die’
It could refer to either ‘Distribution.Simple.Utils.die’,
imported from ‘Distribution.Simple.Utils’ at libraries/Cabal/Cabal/Distribution/Simple.hs:92:11-13
or ‘System.Exit.die’,
imported from ‘System.Exit’ at libraries/Cabal/Cabal/Distribution/Simple.hs:108:1-18
libraries/Cabal/Cabal/Distribution/Simple.hs:417:7:
Ambiguous occurrence ‘die’
It could refer to either ‘Distribution.Simple.Utils.die’,
imported from ‘Distribution.Simple.Utils’ at libraries/Cabal/Cabal/Distribution/Simple.hs:92:11-13
or ‘System.Exit.die’,
imported from ‘System.Exit’ at libraries/Cabal/Cabal/Distribution/Simple.hs:108:1-18
libraries/Cabal/Cabal/Distribution/Simple.hs:591:27:
Ambiguous occurrence ‘die’
It could refer to either ‘Distribution.Simple.Utils.die’,
imported from ‘Distribution.Simple.Utils’ at libraries/Cabal/Cabal/Distribution/Simple.hs:92:11-13
or ‘System.Exit.die’,
imported from ‘System.Exit’ at libraries/Cabal/Cabal/Distribution/Simple.hs:108:1-18
libraries/Cabal/Cabal/Distribution/Simple.hs:641:36:
Ambiguous occurrence ‘die’
It could refer to either ‘Distribution.Simple.Utils.die’,
imported from ‘Distribution.Simple.Utils’ at libraries/Cabal/Cabal/Distribution/Simple.hs:92:11-13
or ‘System.Exit.die’,
imported from ‘System.Exit’ at libraries/Cabal/Cabal/Distribution/Simple.hs:108:1-18

Use import list to hide new System.Exit.die
Soon, System.Exit will export the new `die` (see #9016) which would clash with
Cabal's own `die` implementation. This commit provides forward-compatiblity.
This also updates the Cabal submodule which requires a similiar fix.
Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>

Add System.Exit.die (re #9016)
The original proposal discussion can be found at
http://thread.gmane.org/gmane.comp.lang.haskell.libraries/20872
Note this also updates the Haddock submodule to remove Hadock's local
`die` implementation.

Generalise type of recently added System.Exit.die
This is a follow-up to 77ea2eb0ab36d1a (re #9016) which added `die` with a
return type of `IO ()` even though all other functions in System.Exit have
the more general return type `IO a`. It is assumed this was an oversight in
the original proposal.
Acked-by: Edward Kmett <ekmett@gmail.com>
Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>

I compiled GHC from git with 7.6.3, which worked ok. Now trying to compile GHC from git again, with my newly compiled compiler, I get complaints about:

utils/deriveConstants/DeriveConstants.hs:32:48:
Ambiguous occurrence ‘die’
It could refer to either ‘Main.die’,
defined at utils/deriveConstants/DeriveConstants.hs:880:1
or ‘System.Exit.die’,
imported from ‘System.Exit’ at utils/deriveConstants/DeriveConstants.hs:22:1-18
utils/deriveConstants/DeriveConstants.hs:104:28:
Ambiguous occurrence ‘die’
It could refer to either ‘Main.die’,
defined at utils/deriveConstants/DeriveConstants.hs:880:1
or ‘System.Exit.die’,
imported from ‘System.Exit’ at utils/deriveConstants/DeriveConstants.hs:22:1-18
utils/deriveConstants/DeriveConstants.hs:742:21:
Ambiguous occurrence ‘die’
It could refer to either ‘Main.die’,
defined at utils/deriveConstants/DeriveConstants.hs:880:1
or ‘System.Exit.die’,
imported from ‘System.Exit’ at utils/deriveConstants/DeriveConstants.hs:22:1-18
utils/deriveConstants/DeriveConstants.hs:744:28:
Ambiguous occurrence ‘die’
It could refer to either ‘Main.die’,
defined at utils/deriveConstants/DeriveConstants.hs:880:1
or ‘System.Exit.die’,
imported from ‘System.Exit’ at utils/deriveConstants/DeriveConstants.hs:22:1-18
utils/deriveConstants/DeriveConstants.hs:770:29:
Ambiguous occurrence ‘die’
It could refer to either ‘Main.die’,
defined at utils/deriveConstants/DeriveConstants.hs:880:1
or ‘System.Exit.die’,
imported from ‘System.Exit’ at utils/deriveConstants/DeriveConstants.hs:22:1-18
utils/deriveConstants/DeriveConstants.hs:888:11:
Ambiguous occurrence ‘die’
It could refer to either ‘Main.die’,
defined at utils/deriveConstants/DeriveConstants.hs:880:1
or ‘System.Exit.die’,
imported from ‘System.Exit’ at utils/deriveConstants/DeriveConstants.hs:22:1-18

Harden imports in `DeriveConstants.hs` module
This was generated by applying `-ddump-minimal-imports` and addresses
the current compile failure (see #9016) with GHC HEAD due to the new
`die` being exported by `System.Exit`
Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>